Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/50—Transmitters
  • H04B10/501—Structural aspects
  • H04B10/503—Laser transmitters
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
  • H04B10/071—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using a reflected signal, e.g. using optical time domain reflectometers [OTDR]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
  • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
  • G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
  • G01M11/3118—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using coded light-pulse sequences
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
  • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
  • G01M11/30—Testing of optical devices, constituted by fibre optics or optical waveguides
  • G01M11/31—Testing of optical devices, constituted by fibre optics or optical waveguides with a light emitter and a light receiver being disposed at the same side of a fibre or waveguide end-face, e.g. reflectometers
  • G01M11/3109—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR
  • G01M11/3127—Reflectometers detecting the back-scattered light in the time-domain, e.g. OTDR using multiple or wavelength variable input source
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
  • H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
  • H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
  • H04B10/50—Transmitters

Definitions

• the invention relates to the field of telecommunications, and in particular to a device of and a method for optical data transmission in an optical access network.
• access networks also called passive optical networks (PON) are used, for connecting a plurality of customers to a core network of data transportation.
• PON passive optical networks
• I n such an access network
• the interconnection between the core network and the access network is given at a so-called central office, which contains an optical line terminal (OLT).
• OLT optical line terminal
• the OLT is connected via at least one optical fiber, preferably called optical feeder fiber, to a so-called remote node.
• an optical downlink signal transmitted by the OLT is split onto different optical branches, to which one or more customers are connected by means of optical network units (ONU).
• ONU optical network units
• the customers send via the optical branches optical uplink signals towards the remote node, which combines these optical uplink signals to a combined uplink signal and transmits this via the optical feeder fiber to the optical line terminal.
• a measurement technique of optical time domain reflectometry can be applied.
• OTDR optical time domain reflectometry
• a reflection profile of the transmission channel is estimated.
• the technique of OTDR is carried out at the OLT.
• a measurement signal in the form of an optical pulse may be transmitted into the optical channel.
• the received response signal which is reflected by the optical channel, can then be traced in the time domain, for determining the reflection profile.
• a measurement signal may be generated as an optical signal carrying a correlation sequence.
• the received response signal is then recorded and used for determining the reflection profile.
• the reflection profile can be determined, by correlating a sampled version of the received response signal with the initial correlation sequence itself.
• the auto-correlation function of the correlation sequence is equal to or approximated by the dirac delta function, the result of the correlation yields an estimate of the impulse response of the optical channel in the time domain, which is an approximation of the reflection profile.
• the transmission device and the separate OTDR device are in this case both coupled to the same optical channel, preferably via an optical coupler.
• the optical channel is preferably an optical fiber connected to the devices.
• a more advanced technique is that of embedded OTDR, in which the transmission device itself contains the hardware for generating the optical transmission signal as well as the hardware that is necessary for carrying out an OTDR measurement.
• the optical transmission signal is directly modulated in dependence on a correlation sequence, wherein the frequency of this direct modulation is chosen such that it does not disturb data reception at a receiving side.
• the response signal of the optical channel can be obtained, by filtering out from received optical signal that frequency, at which the optical transmission signal was modulated.
• This received response signal can then be used for determining a reflection profile via the technique of signal correlation as it has been described previously above.
• the device comprises a laser transmission unit, which is operable to generate an optical transmission signal. Furthermore, the device comprises a driving unit, which is operable to control the laser transmission unit, such that the optical transmission signal is modulated in dependence on a data signal, which is preferably an electrical data signal.
• the device comprises an optical reception unit, which is adapted to convert at least a fraction of a received optical signal into an electrical measurement signal.
• the optical reception unit contains and makes use of a photo-diode and an electrical amplifier, which are both an integral part of the optical reception unit.
• the optical reception unit is furthermore separate from the laser transmission unit.
• the device comprises furthermore at least one control unit, which is operable to control the laser transmission unit, such that the optical transmission signal is modulated in dependence on a measurement signal.
• the control unit is furthermore operable to measure multiple electrical measurement signals during a measurement interval and to determine an averaged received electrical
• control unit is operable to control the electrical amplifier, such that the electrical amplifier is turned off during at least a fraction of a time interval, which is prior to the measurement interval.
• this optical signal may have a fixed wavelength with a narrow line width, preferably called bandwidth.
• the wavelength is fixed, in the sense that for a given constant temperature of the laser transmission unit also the wavelength is constant.
• the electrical amplifier By turning the electrical amplifier off during a time interval prior to the measurement interval, and then turning the electrical amplifier on for the time of the measurement interval, the electrical amplifier will generate thermal energy within the optical reception unit. This thermal energy may then dissipate from the optical reception unit to the laser transmission unit, where it then may cause a temperature change and thus also a change of the optical center wavelength at which the laser transmission unit generates the optical transmission signal.
• the change of the optical signal's center wavelength used for data transmission as well as OTDR measurement will in turn reduce the impact of coherent Raleigh noise onto the measurement during the measurement interval.
• the proposed device has the advantage, that no extra thermoelectric cooler or thermoelectric heater has to be foreseen within or directly at the laser transmission unit for changing the temperature in order to change the center wavelength of the generated optical signal.
• the thermal energy of the electrical amplifier can be used for this.
• Figure 1 shows a proposed optical transmission device according to an embodiment.
• Figure 2 shows alternating time intervals of measurement and non-measurement.
• Figure 1 shows an optical transmission device OTD, which is preferably used within an optical line terminal of an optical access network.
• the device OTD contains a laser transmission unit LD, which is preferably a laser diode.
• the laser transmission unit LD is a semiconductor laser, which may be in a preferred embodiment a distributed feedback (DFB) laser.
• the transmission unit LD generates an optical signal OS, which has a center wavelength and a line width.
• the optical signal OS is transmitted into an optical sub assembly OSA.
• the optical signal OS passes an optical isolator I as well as an optically partially transmitting device M and an optical filter F towards an optical interface OIF, at which preferably a lens L is located.
• the optical interface OIF may contain a plug for connecting an optical fiber, or as an even further alternative a so call fiber pigtail.
• the optical isolator I transmits optical signals propagating from the transmission unit LD towards the lens L, while it suppresses a transmission of optical signals propagating from the lens L towards the transmission unit LD.
• the optically partially transmitting device M is preferably an optically partially reflecting mirror, which allows a greater fraction of the signal OS to propagate in the direction from the transmission unit LD towards the lens L, while it reflects a smaller fraction of the signal OS propagating in this direction. Furthermore, this mirror allows a greater fraction of an optical signal to propagate from the lens L towards the transmission unit LD, while it reflects a smaller fraction of such a signal propagating in this direction. As an example, 90 % of the energy of an optical signal are transmitted by the optically partially reflecting mirror, while 1 0 % of the energy of an optical signal are reflected by the optically partially reflecting mirror.
• the optically partially transmitting device M is alternatively an optical wavelength division multiplex (WDM) tap coupler.
• WDM optical wavelength division multiplex
• Such a tap coupler transmits optical signals in the direction of the optical signal OS for first predefined wavelength or wavelength range, while it suppresses transmission optical signals in this direction for a second predefined wavelength or wavelength range.
• the first predefined wavelength is coincident with the wavelength of the optical signal OS.
• the tap coupler transmits optical signals in the direction from the lens L towards the transmission unit LD for the second wavelength or wavelength range, while it directs optical signals coming from the lens L towards the reception unit ORX for the first predefined wavelength or wavelength range.
• the optical filter F allows optical signals to propagate from the transmission unit LD towards the lens L.
• the filter F filters optical signals propagating from the lens L towards the filter F in the way, that optical signals having the wavelength of the transmitted optical signal OS pass the filter F towards the optically partially transmitting device M, while optical signals of a different wavelength are reflected by the filter F towards an optical data reception unit ODRX.
• the optical transmission signal OS is a downlink signal with a wavelength of 1 490 nm
• an optical uplink signal OUS which is preferably a combined uplink signal, received at the device OTD, preferably from other units of a network, has a wavelength of 1 31 0 nm.
• the optical transmission device OTD is connectable at the lens L to an optical fiber OF, into which the device OTD transmits the transmission signal OS and receives the optical uplink signal OUS.
• the lens L can be seen as an optical interface of the device OTD.
• the laser transmission unit LD is controlled by a driving unit LDU, such that the optical transmission signal OS is modulated in dependence on an electrical data signal.
• the electrical data signal is preferably received at the device OTD via a data interface DTX.
• the control unit OC controls the laser transmission unit, LD, such that the optical transmission signal OS is modulated in dependence on a measurement signal.
• the measurement signal is preferably a digital electrical signal representing a correlation sequence.
• the laser driving unit LDU provides an electrical bias signal to the transmission unit LD for power adjustment as well as an electrical modulation signal for modulating the optical signal OS in dependence on digital data received at the driving unit LDU.
• This data is preferably received at the device OTD via a data interface DTX.
• the laser driver LDU itself is controlled by a control unit MC, which is preferably a micro controller, wherein the unit MC controls a working point of the driving unit LDU. Furthermore, the unit MC controls the driving unit LDU, such that temperature compensation is carried out.
• a control unit MC which is preferably a micro controller, wherein the unit MC controls a working point of the driving unit LDU. Furthermore, the unit MC controls the driving unit LDU, such that temperature compensation is carried out.
• the modulation of the transmission signal OS in dependence on the measurement signal is preferably carried out, by using as a correlation sequence a pseudo-random bit sequence.
• This bit sequence has a pre-defined bit rate, which is preferably a bit rate of 1 0 MHz.
• the bit sequence has preferably a length of 2" - l .
• the device OTD receives from the fiber OF at the lens L a response signal ROS of the optical channel. This signal ROS then passes the optical filter F. A fraction FROS 1 of this signal ROS is reflected or suppressed by the optically partially transmitting device M towards an optical reception unit ORX. A remaining fraction FROS2 of the signal ROS is transmitted by the optically partially transmitting device M towards the isolator I, which suppresses this remaining fraction FROS2, such that it does not reach the laser unit LD.
• the signal fraction FROS1 has a wavelength that is coincident with the first predefined wavelength or wavelength range, while the signal fraction FROS 2 has wavelength that is coincident with the second predefined wavelength or wavelength range.
• the laser transmission unit LD is controlled by a control unit OC, such that the transmission signal OS is modulated in dependence on a measurement signal.
• the fraction FROS1 of the received optical signal is converted into an electrical measurement signal EMS.
• the reception unit ORX contains a photo diode PD, which converts the signal fraction FROS1 into an electrical signal, as well an amplifier TIA, which amplifies the converted electrical signal for obtaining the electrical measurement signal EMS.
• the amplifier TIA is preferably a transimpedance amplifier.
• the amplifier TIA uses preferably electrical energy provided by a power supply PS.
• the modulation of the transmission signal OS in dependence on the measurement signal is preferably an amplitude modulation.
• the modulation of the optical signal OS in dependence on the received data is also an amplitude modulation at a predefined bit rate using on and off keying. This on and off keying is preferably carried out at a bit rate of 2.5 Gigabits per second.
• measurement signal is preferably within the range of 5 to 1 0 % of the optical signal's OS maximal amplitude.
• the measurement signal is modulated onto the optical signal OS successively multiple times.
• the optical reception unit ORX thus measures multiple electrical measurement signals, by converting a fraction of the received optical signal FROS1 to these respective electrical measurement signals.
• the multiple electrical measurement signals are then provided to an OTDR control unit OC, which stores these multiple electrical measurement signals and determines an average received electrical measurement signal based on the measured electrical signals.
• This averaging may be an unweighted or a weighted averaging.
• the averaged received electrical measurement signal determined within the control unit OC may then be provided via a data bus I2C to a device, not explicitly shown in Figure 1 .
• a device may the correlate the averaged measurement signal with the correlation sequence itself for finally determining a reflection profile of the optical channel.
• this correlation may be carried out directly within the control unit OC.
• the control unit MC controls the amplifier TIA, such that the amplifier TIA is turned off during at least a fraction of a time interval prior to the measurement interval.
• control unit MC is connected to a power supply PS of the amplifier TIA via an electrical connection.
• control unit MC sends an electrical control signal CS, also shown as "TIA enable", to the power supply PS.
• CS electrical control signal
• the amplifier TIA is turned on and off in dependence on the control signal CS sent by the control unit MC.
• control unit MC is connected electrically directly with the amplifier TIA, wherein the amplifier TIA provides an interface, preferably a PIN-connection not explicitly shown in Figure 1 , at which an electrical control signal can turn the amplifier TIA directly on and off.
• the amplifier TIA will generate thermal energy when it is turned on.
• the amount of thermal energy present within the reception unit ORX can be varied.
• the thermal energy present within the reception unit ORX may dissipate from the reception unit ORX towards the separate laser transmission unit LD.
• the amount of thermal energy present within the transmission unit LD due to thermal energy dissipation can be varied.
• a change or variation of the center wavelength of the optical transmission signal generated by the transmission unit LD can be achieved.
• the reception unit ORX and the laser transmission unit LD are separate in the sense, that they have respective casings that are not directly connected to each other. These casing may preferably be indirectly connected to each other via a casing of an optical sub assembly (OSA), which will be described in detail further below.
• OSA optical sub assembly
• Figure 2 shows different time intervals of measurement and non-measurement.
• the amplifier for measuring the electrical measurement signals within the reception unit has to be turned on only during such time intervals, during which a measurement of the reflection profile shall be carried out.
• a measurement interval I I measurement is carried out and therefore, the amplifier is turned on.
• the time interval 10 of non-measurement no OTDR measurement is to be performed, and thus the amplifier is turned off during this time interval of non-measurement.
• the amplifier does not have to be turned off during the whole time interval 10, but may preferably be turned off only during a fraction the time interval 10 of non-measurement.
• a number of 2 18 correlation sequences are transmitted, such that an averaged electrical measurement signal is based on 2 18 individual electrical measurement sequences.
• the time interval I I of measurement is followed by another time interval 12 of non- measurement, which then is followed by a further time interval 13 of measurement.
• the control unit controls the amplifier, such that it is turned off during at least a fraction of the time interval 12.
• the amplifier is turned on under control of the control unit.
• the turning on and off of the amplifier TIA during the respective time intervals may be carried out by a software task running on the control unit MC.
• control unit MC is preferably a micro controller
• control unit OC is preferably implemented as an application specific integrated circuit (ASIC).
• ASIC application specific integrated circuit
• control units MC and OC may be provided as separate control units or alternatively as one control unit.
• the control units OC und MC may be implemented as a common control unit or separate control units relying on different combinations of hardware and/or software.
• the optical subassembly OSA is optically connected to the laser transmission unit LD and the optical reception unit ORX.
• the optical subassembly OSA is able to provide the optical transmission signal OF to an optical interface OIF, preferably given by the lens L.
• optical subassembly OSA is able to receive the received optical signal ROF from the optical interface OIF.
• the optical subassembly OSA is preferably a hermetically sealed device with a casing CA. To this casing, the transmission unit LD and the reception unit ORX are mechanically connected. Furthermore, also an optical data reception unit ODRX is mechanically connected to the subassembly OSA.
• the optical sub-assembly may have a casing CA made of plastic.
• the casing CA of the subassembly OSA is a metallic casing, which provides the advantage of allowing a faster thermal energy dissipation from the reception unit ORX towards the transmission unit LD. This is especially of advantage in the case, that the reception unit ORX and the transmission unit LD are both sealed in respective metallic cases CA1 , CA2, which are welded to the casing CA of the subassembly OSA.
• the transmission unit OTD contains preferably the optical data reception unit ODRX, which receives data via the uplink signals OUS.
• the optical data reception unit ODRX may also make use of a photo diode as well as an amplifier for deriving from the optical uplink signal OUS received data, which then may be provided to a data interface DRX.
• the proposed device discloses also a method of optical data transmission, as claimed in an independent claim, which comprises different steps corresponding to the independent claim claiming the proposed device.
• control unit' may be provided through the use of dedicated hardware as well as hardware capable of executing software in association with appropriate software.
• the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared.
• explicit use of the term 'control unit' should not be construed to refer exclusively to hardware capable of executing software, and may implicitly include, without limitation, digital signal processor (DSP) hardware, application specific integrated circuit (ASIC), field programmable gate array (FPGA), read only memory (ROM) for storing software, random access memory (RAM), and non volatile storage.
• DSP digital signal processor
• ASIC application specific integrated circuit
• FPGA field programmable gate array
• ROM read only memory
• RAM random access memory
• non volatile storage Other hardware, conventional and/or custom, may also be included.

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• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Optics & Photonics (AREA)
• Chemical & Material Sciences (AREA)
• Analytical Chemistry (AREA)
• General Physics & Mathematics (AREA)
• Optical Communication System (AREA)
• Light Receiving Elements (AREA)

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• 2012
  • 2012-05-29 EP EP12305591.5A patent/EP2670068B1/en not_active Not-in-force
• 2013
  • 2013-04-19 IN IN9435DEN2014 patent/IN2014DN09435A/en unknown
  • 2013-04-19 CN CN201380027942.2A patent/CN104350371B/zh not_active Expired - Fee Related
  • 2013-04-19 US US14/399,330 patent/US9287989B2/en not_active Expired - Fee Related
  • 2013-04-19 KR KR1020147036329A patent/KR101562159B1/ko not_active Expired - Fee Related
  • 2013-04-19 JP JP2015514392A patent/JP5977445B2/ja not_active Expired - Fee Related
  • 2013-04-19 WO PCT/EP2013/058132 patent/WO2013178403A1/en active Application Filing
  • 2013-04-30 TW TW102115442A patent/TWI508470B/zh not_active IP Right Cessation

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